The sealing faces of mechanical shaft seals are extremely important to the integrity of such seals. To establish and ensure a fluid-tight seal, the sealing faces between the abutting sealing members of a mechanical seal must be maintained as planar as possible. For example, there are applications for mechanical seals requiring that the surface flatness of the abutting seal faces to be within three light bands. Thus, anything which may disrupt seal face flatness may debilitate seal performance.
The finish or smoothness of the seal faces is also extremely important to the proper functioning of a mechanical seal. Scratches or other blemishes on the seal surfaces which are damaging to the finish thus can be detrimental to seal performance. Scratch depths as little as several microinches can be sufficient to facilitate seal leakage.
Contaminants in the fluid to which a mechanical shaft seal is subject can seriously damage seal face integrity. Often such contaminants include particles of sufficient size and hardness to damage the seal faces if the particles become positioned between the abutting seal faces. Although some protection against particle damage to the seal faces is provided by selecting proper materials for the seals, this protection can be expensive and difficult to accomplish effectively. With seal component wear and long exposure to fluid under pressure which bears contaminants, some particulate material is likely to reach the sealing surfaces of a mechanical seal. Therefore, there is need for a mechanical means for inhibiting potential seal damaging particles from reaching the seal faces of a mechanical seal.
Also, during the normal operation of a mechanical seal, the seal faces will ultimately wear due to friction therebetween. To prevent unexpected failure of the seal, there is need to monitor such seal face dissipation so that potential seal failure can be anticipated. Heretofore, such failure has been signalled by increasing leakage.